Field of the Invention
This invention relates to power supplies. Specifically, and not by way of limitation, the present invention relates to an uninterruptible power supply for an electric apparatus.
Description of the Related Art
An uninterruptible power supply (UPS) or uninterruptible power source is an electrical device which provides emergency power to a load for an electrical apparatus when the primary input power source, typically AC main power fails. A UPS differs from a standby generator or an auxiliary power system in that the UPS provides near-instantaneous protection from input power interruptions, by supplying energy stored in batteries to the load. The battery runtime for most uninterruptible power sources is relatively short, e.g., a few minutes, but is sufficiently long to start a standby power source or properly shut down the protected electrical apparatus.
A UPS unit is typically used to protect electrical hardware such as computers, data centers, or other electrical equipment where an unexpected power disruption could cause injuries, fatalities, serious business disruption or data loss. UPS units range in size from units designed to protect a single computer without a video monitor to large units powering entire data centers or buildings.
FIG. 1 is a simplified block diagram of an existing UPS unit 10 providing alternating current (AC) power normally to an electrical apparatus. In its most simplified form, the existing UPS unit 10 typically includes an AC electrical source 12, such as from a typically main electrical system of a building or home. The AC electrical source 12, under normal circumstances, provides power to an electrical apparatus 14. The UPS unit also includes a charger 16, a battery 18, and an inverter 20. In addition, the UPS unit 10 includes an inverter switch 22 and a main power switch 24. As depicted in FIG. 1, the charger, battery and inverter are disconnected from the electrical apparatus 14. The battery 18 receives power through the charger 16 from the AC electrical source 12.
FIG. 2 is a simplified block diagram of the existing UPS unit 10 of FIG. 1 during a power loss or disruption of acceptable power to the electrical apparatus 14. When the incoming voltage from the AC electrical source 12 falls below or rises above a predetermined level, the UPS unit 10 turns on its internal DC-AC inverter circuitry 30, which is powered from the battery 18. This provides high or low voltage protection to the electrical apparatus. The UPS unit 10 then switches power to the DC-AC inverter circuitry 30 by moving the switches 22 and 24 to use the battery to power the electrical apparatus. As the battery using direct current (DC) power, the power is converted to AC power through the use of the inverter 20. The objective of the UPS is to power electrical equipment, such as a personal computer, without any objectionable dip or brownout to that device.
Although the UPS unit 10 depicted in FIGS. 1 and 2 are useful, existing UPS units suffer from several drawbacks caused by using an inverter. The traditional UPS unit uses a low voltage DC supply converted into high voltage AC power through a core step-up transformer augmented with an oscillator to manage waveform in hertz. With the requirement of converting DC power to AC power for the electrical apparatus 14, the UPS unit 10 typically creates a large footprint to accommodate the use of an inverter. Additionally, excess amounts of heat are generated by converting the DC power to AC power. This increase in heat is a severe problem which requires additional cooling devices and design configurations to reduce the heat signature of the UPS unit 10. In addition, the inverter provides a “step up” in power, which further contributes to the complexity and cost of the UPS unit. Furthermore, the existing UPS requires a high capacity inverter and complex circuitry with AC/DC and vice versa conversion requirements.
It would be advantageous to have a UPS unit which provides simple and efficient power switchover from the AC electrical source to a battery without the complexity and inherent problems associated with existing UPS units. It is an object of the present invention to provide such an apparatus.